I. Field of the Invention
The present invention relates to a device for stretching pipe. More specifically, the present invention relates to a novel and improved apparatus for stretching spiral ribbed pipe having a circular end cross-section into pipe having an elliptical or oval end cross-section.
II. Background Art
Heating and air condition installations in commercial buildings have typically used the conventional rectangular or square flat wall ducting or pipe for conducting air to and from locations within the building. The size of the ducting is chosen according to the building air flow design specifications. The rectangular ducting is the most commonly used in commercial application. This type of flat wall ducting must have a wall thickness sufficient to maintain structural integrity and the rectangular cross-section of the ducting than cylindrical ducting. In addition, the rectangular or square ducting has a larger surface area than cylindrical ducting so that more metal is used in the manufacture of rectangular or square ducting than the cylindrical ducting. The increase in wall thicknesses and surface are translated in the requirement that more be used in the manufacture of rectangular or square ducting than that in cylindrical ducting. Coupled with the additional manufacturing difficulty in fabricating rectangular ducting, this type of ducting is more expensive than comparable cylindrical ducting.
In many applications it is desirable to use a corrugated cylinder ducting which requires less metal in its manufacture and is, therefore, less expensive. Less metal is required in corrugated cylindrical ducting because of the less surface area and thinner walls which may be used since the ribs increase structural support. In addition, the corrugated cylindrical ducting requires less labor in its manufacture. Although the construction of the cylindrical spiral ribbed ducting is advantageous on a cost per foot basis, its cross-sectional shape limits its use in many applications where only rectangular or square ducting would fit.
It is, therefore, an object of the present invention to provide an apparatus for stretching spiral ribbed ducting having a cylindrical cross-section into ducting having an oval or elliptical cross-section.